Nano-TiO2 particles prepared by the sol-gel method were used as catalyst for the degradation of nitrobenzene by ozone. Catalyst samples were characterized by measuring the specific area (SBET), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Removal efficiency of nitrobenzene (NB) was significantly promoted in the presence of catalyst compared with ozone alone. TiO2 calcined at 500 degrees C showed the best activity. Different experimental conditions like catalyst dose, ozone dosage, initial nitrobenzene and pH have been examined. The mechanism of catalytic ozonation was also discussed. Both ozonation and catalytic ozonation were significantly influenced by carbonate and tert-butyl alcohol, which confirmed that TiO2-catalyzed ozonation follows a radical-type mechanism. And hydroxyl radicals were truly identified by spin-trapping/EPR technique. (C) 2006 Elsevier B.V All rights reserved.